How would you design a Payment Gateway integration that supports multiple providers (PayPal, Stripe)?
Provider-Agnostic Payment Gateway Design
I would define an application-level payment abstraction and implement one adapter per provider. The business layer should work with our own PaymentRequest and PaymentResult models rather than provider-specific SDK types. A factory or dependency-injection strategy can select the appropriate provider. This isolates vendor-specific APIs and makes adding another provider much safer.
- 1
Use an abstraction owned by the application rather than exposing provider SDK types.
- 2
Use Adapter implementations to translate provider-specific APIs.
- 3
Select providers through dependency injection, configuration, routing policy, or a factory.
- 4
Normalize provider errors into meaningful application-level error categories.
- 5
Design for idempotency because payment requests may be retried.
- 6
Handle webhooks, asynchronous payment states, timeouts, retries, reconciliation, and duplicate notifications.
- 7
Never assume a successful API response alone means the entire payment lifecycle is complete.
Follow-up Questions
- How would you implement payment idempotency?
- How would you handle provider timeouts?
- How would you design payment webhooks?
- How would you add automatic provider failover?